The infectious laryngotracheitis virus (ILTV) is an alphaherpesvirus (B. Roizman, Arch. Virol. 1992. 123. 425-449) which causes a major respiratory pathology (infectious laryngotracheitis or ILT) in chicken (L. E. Hanson and T. J. Bagust, Diseases of Poultry 9th edn 1991. pp 485-495. Ames, Iowa State University Press). The vaccines currently available against this condition contain an attenuated strain which can be administered by various routes including the intranasal, conjunctival and cloacal routes, in drinking water and by aerosol (L. E. Hanson and T. J. Bagust (1991).
Studies of the molecular biology of the ILTV virus have made it possible to characterize the viral genome (M. A. Johnson et al., Arch. Virol. 1991. 119. 181-198) and to identify some of the virus genes (A. M. Griffin, J. Gen. Virol. 1989. 70. 3085-3089) including the genes encoding thymidine kinase (UL23) (A. M. Griffin and M. E. G. Boursnell, J. Gen. Virol. 1990. 71. 841-850; C. L. Keeler et al., Avian Dis. 1991. 35. 920-929), the glycoprotein gB (UL27) (A. M. Griffin, J. Gen. Virol. 1991. 72. 393-398; K. Kongsuwan et al., Virology 1991. 184. 404-410; D. J. Poulsen et al., Virus Genes 1991. 5. 335-347), the glycoprotein gC (UL44) (D. H. Kingsley et al., Virology 1994. 203. 336-343), the capsid protein p40 (UL26) (A. M. Griffin, Nucl. Acids Res. 1990. 18. 3664), the protein homologous to the ICP4 protein of herpes simplex (HSV-1) (M. A. Johnson et al., Virus Research 1995. 35. 193-204), the proteins homologous to the proteins ICP27 (UL54), glycoprotein gK (UL53) and DNA helicase (UL52) from HSV-1 (M. A. Johnson et al., Arch. Virol. 1995. 140. 623-634), ribonucleotide reductase (A. M. Griffin, (1989); and WO-A-90/02802), the UL1 to UL5 genes (W. Fuchs and T. C. Mettentleiter, J. Gen. Virol. 1996. 77. 2221-2229), the genes present in the short unique sequence of the genome (U.sub.s) (M. A. Johnson et al., DNA Sequence--The Journal of Sequencing and Mapping 1995. Vol. 5. pp 191-194; K. Kongsuwan et al., Arch. Virol. 1995. 140. 27-39; K. Kongsuwan et al., Virus Research 1993. 29. 125-140; K. Kongsuwan et al., Virus Gene 1993. 7. 297-303; M. A. Wild et al., Virus Genes 1996. 12. 107-116; WO-A-92/03554; and WO-A-95/08622).